In recent years, the Internet with computer networks connected each other has been rapidly in wide use, thereby various services such as email, net news, download of moving picture or audio data and TV conference system have been supplied. The supplying of the various services is mainly supported by the enhancement in performance of computer and the progress of network communication technology. As the various services become widely used, terminal units to use the service have become also multiform. For example, as the multiform terminal units, there are home-use personal computers through conventional public telephone line, office-use computers through broadband dedicated line, and portable terminal units such as a personal digital assistant (PDA) and a cellular phone through wireless communication line.
In using the various services on the Internet, it is necessary to set the communication line between a terminal unit and an application server to supply the various services on the Internet. In this regard, the setting of communication bandwidth is conducted so that the resource in network can be used effectively and thereby the terminal unit subject to the service can be comfortably serviced. Thus, the various service data are transferred from the application server.
In setting the communication bandwidth, it is necessary to know the bandwidth of line between the application server and the terminal unit. Therefore, in conventional network systems, for example, bandwidth information is sent from the terminal unit to the application server, and through a communication line to be set based on this information, various service data are transferred from the application server to the terminal unit.
On the other hand, Japanese patent application laid-open No. 11-112543 (1999) discloses a data communication method and a repeater used in the method. In the network system to which this method is applied, in order to conduct the data transfer using an optimum bandwidth, the repeater that stores in advance communication bandwidths to be set to respective communication identification information secures a communication bandwidth according to the communication identification information of repeating data received. Thereby, sending the bandwidth information and further installing a specific bandwidth securing protocol becomes unnecessary.
However, in the conventional network system that bandwidth information is sent before the start of communication, the terminal unit has to be equipped with an additional unit for sending the bandwidth information. So, there is a problem that the system prevents the mobile terminal from being miniaturized and lightened and lays all of various terminals such as the existing Internet system under need for being equipped with the like function.
Also, it is practically difficult to apply the technology disclosed in Japanese patent application laid-open No. 11-112543 to a network composing the existing Internet. Because, especially in case of the Internet with various networks connected each other, all the networks, not a specific network, need to be adapted to the technology.
On the other hand, concerning the various networks connected each other in the Internet, the communication bandwidth between them is broad. In contrast, the line between the terminal unit and an access server included in the Internet for connection with this terminal unit is of narrow bandwidth. Therefore, the bandwidth of communication line to be set between the terminal unit and the application server often depends on the bandwidth of line between the terminal unit and the access server. Namely, if the bandwidth of line between the terminal unit and the access server were known, the resource in network would be used effectively and thereby the terminal unit subject to the service would be comfortably serviced, so that the various service data could be transferred from the application server.